土地利用及养分条件对温带草地土壤有机碳固持及稳定性的长期影响

Soil organic carbon (SOC) is an essential component of soil physical-chemical properties, and it is also the dominate indicator for soil quality. Soil carbon sequestration potential depends on SOC sequestration and its stability, which can be influenced by land use and soil nutrient condition. However, the mechanisms of SOC sequestration and its stability in response to land use and nutrient condition for long term remain unclear. To address this issue, this project will perform a two factors experiment including land use type (mowing vs unmowing) and nutrient condition (control, nitrogen addition, phosphorus addition, nitrogen and phosphorus addition) in a temperate steppe of China. Through defining soil aggregate classes and isolating soil carbon fractions, as well as the application of synchrotron radiation soft X-ray spectroscopy to qualitative and semi-quantitative analyze SOC chemical structure, study the responses of SOC and its fractions to land use and nutrient condition. Coupling the responses of plant community structure and function characteristics, this study will reveal the relationship between SOC and vegetation characteristics, and exhibit the mechanisms of SOC sequestration and its stability in response to land use and nutrient condition. This research will provide a new basis to further study on soil carbon sequestration and its stability mechanism in response to global change, and have valuable implications for the sustainable and adaptive management of the temperate steppe in China.

土壤有机碳(SOC)是土壤最基本的要素，也是重要的土壤质量指示因子。土地利用及养分条件对SOC固持及稳定性的长期影响直接关系着土壤固碳潜力的评估与预测。但是，当前草地生态系统SOC固持及其稳定性对土地利用及养分条件变化的长期响应机理尚不清楚。本项目拟以我国温带草地为研究对象，利用已建立的土地利用(对照、割草)和养分条件(对照、氮添加、磷添加和氮磷添加)控制实验平台，通过对土壤团聚体颗粒分级及对SOC组分进行区分，并应用同步辐射软X-射线光谱技术对SOC化学结构进行定性和半定量分析，揭示SOC组分及结构对土地利用及养分条件的响应规律；并结合群落特征及植物功能性状等植被特征的变化，探究SOC组分及结构与植被特征的关系，阐明土地利用及养分条件对SOC固持及稳定性的长期影响机制，为全球变化情景下土壤固碳特征及其稳定性机制研究提供新的依据，同时也为我国温带草地适应性管理提供决策支持。

草地主要分布在干旱半干旱区，在调节全球陆地碳循环中发挥着重要作用。然而，当前关于全球变化如何影响草地生态系统碳库的结果仍不明确。本项目以内蒙古典型温带草地为研究对象，采用割草和氮素添加的处理方法，研究土地利用及养分条件对土壤碳固持及组分的影响，旨在量化半干旱草地生态系统碳源汇功能，并探索与之相关的植物功能性状特征。研究结果表明1）割草及氮素添加对大团聚体含量、微团聚体含量、<0.053 mm粒径级含量、几何平均直径以及团聚体各组分碳氮含量均无影响。2）植物地上生物量、碳库、氮库在割草处理下分别显著降低了14.3%、17.3%和12.1%。氮添加处理地上生物量和凋落物分别增加了28.8%和77.4%，同时氮素的添加提高了植物氮含量和氮库。3)氮添加显着降低群落、多年生杂类草、多年生禾草和一二年生植物的幼苗密度，随着氮素添加水平的增加群落、多年生杂类草和一二年生植物物种数急剧下降，但多年生禾草物种数没有变化。结果表明蒙古高原温带草地植物碳库对割草和氮添加的响应比土壤碳库更敏感。项目研究结果有助于准确估算我国陆地碳源汇功能、为维持面积广阔的天然草原生态系统服务功能的决策制定提供数据支持和理论依据。